BOSTON, MA (WCVB/CNN) – In Boston, a set of twins born 24 days apart are healthy, thanks to the efforts of doctors who performed a rare surgery to save both children.

They are twins, but they don’t share a birthday. In fact Alexandre is more than 3 weeks older than his brother Ronaldo. Both boys are thriving after a rare and risky delayed delivery that has exceeded every expectation.

“This was unique in many ways– including that both twins are doing well,” Sabrina Craigo, M.D., Tufts Medical Center said.

The challenge began when mom Linda DaSilva went into labor only 24 weeks into her pregnancy. Doctors at Tufts tried to stop the contractions. But 4 days later, a very premature Alexandre was born.

“We were praying to hear his cry.. And we did.. And it was a relief.. Because knew there was 50 percent chance of not surviving,” DaSilva said.

Doctors here placed baby number one in intensive care, and told mom and dad it was time to consider keeping baby number two in mom’s womb a little longer.

“I thought it was absurd! I said I don’t think– I didn’t know this was possible,” DaSilva said.

But doctors explained a “delayed twin delivery” could be done, and DaSilva was a perfect candidate.

“He’s like leave him there- he is fine– his heart is beating well– so okay- then we start praying,” dad Ronaldo Antunes said.

A healthy Ronanldo would be born 24 days later, weighing in a full pound more than his big brother.

“We try to tell moms be grateful for everyday you’re still pregnant and we can get you as far along as we possibly can and this is just a perfect example,” Gina Geis, M.D., Tufts Medical Center NICU said.